The bicycle is perhaps the most widely known form of transportation in the world today. It is used for transportation, recreation, fitness, and business in nearly every part of the world. In the U.S., the total industry volume (bikes, parts, and accessories) in 1972 was estimated at $700 million annually. The bicycle institute of America estimated that in 1972, there were around 85 million bicycle users in the U.S. and that bicycles outsold automobiles, 13 million to 11 million. When compared to its use in the United States, the bicycle's use in Europe is startling. The streets of European cities are often filled with commuters on bicycles, greatly outnumbering the automobiles on the road. In China, nearly 200 million people (50% of the work force) commute to their jobs on bicycles. Bicycles there replace automobiles in filling up the cities' parking lots.
A field of research that has been conducted for over a century but which has seen little success is that of alternative leg motions for power input. When using a rotary crank mechanism, the leg must apply force in varying directions to complete one revolution of the chain ring. At the top and bottom of the stroke, a purely horizontal force is required to maintain motion of the crank. For about 20 degrees on either side of these "dead" spots (about 80 degrees out of the total 360) the horizontal force required to propel the crank is far greater than the vertical force. It is obvious that one can push down with the leg with a much greater force than one can push forward. Thus, these 80 degrees are being wasted in power transfer to the rear wheel. For certain people, such as those with artificial legs or those with limited motion or flexibility of the knee, a forward motion of the leg can be nearly impossible while a downward motion is relatively easy. Thus a mechanism which would only require linear vertical motion of the pedals would be highly desirable because it would not only be more efficient, it would tailor to a larger market of people. Some studies have shown that there may be biomechanical advantages to using an elliptical pedal motion rather than a circular motion or a linear motion. An elliptical pedal motion can give the advantage of using primarily vertical motion with small amounts of horizontal motion at the top and bottom of the pedal stroke while providing a more natural and comfortable leg motion than a linear pedal motion would. Because some bicyclists may prefer a linear pedal motion and some may prefer an elliptical motion, it would be desirable to provide a pedal mechanism which can be converted to provide either linear or elliptical reciprocating pedal motion.
The common rotary crank mechanism has withstood the test of time as the primary form of power transfer device. Although research has shown that a linear movement of the leg is more efficient, a device has not been created that can match the rotary crank in terms of simplicity and effectiveness for transferring the power. Reports dating back as early as 1968 show that cyclers were very interested in departing from the normal rotary crank systems. However, no manufacturer has been able to satisfy the cycler with a durable, compact, efficient mechanism for an alternate leg motion. Previous attempts at alternative motions have been very complex systems of levers, clutches and gears. A rotary crank, on the other hand is very durable and easy to build and maintain. To date, the rotary crank is still used on every major brand of bicycle in production.
One attempt at an alternate leg motion for propelling a bicycle is described in Klopfenstein U.S. Pat. No. 4,561,668. This bicycle allows the leg to move through a slightly curved motion over a range of about 165 degrees. Tests from the developer show an increase in output torque when compared to a normal rotary crank system. However, the complexity of the system, consisting of several linkages and clutches, has hindered the acceptance of the mechanism.
Another alternate drive mechanism is described in Lenhardt U.S. Pat. No. 4,564,206. This drive uses a complicated 5 bar mechanism to allow the pedals to move in an arcuate path.
Pollard U.S. Pat. No. 4,019,230 describes a mechanism which uses one way clutches to allow for a reciprocating arcuate movement of the pedals.
Trammell U.S. Pat. No. 3,779,099 describes a mechanism which is driven by long lever arms connected to a linkage which is attached to one way clutches. This device allows for movement only in a 180 degree path but is still circular in motion.